1. Field of the Invention
The present invention generally relates to heat treatment apparatus and, more particularly, to a heat treatment apparatus applying a heat treatment to a semiconductor substrate and a method for designing such a heat treatment apparatus and a computer readable recording medium storing such a design method.
2. Description of the Related Art
In heat treatment apparatuses, such as a chemical vapor deposition (CVD) apparatus, an annealing apparatus, etc. for forming a semiconductor integrated circuit on a wafer, a wafer is heated by irradiating a light from a heat source. In order to always make temperature of the heated wafer uniform, the wafer is rotated in a predetermined plane facing the heat source during heating.
FIGS. 1A and 1B are views showing a composition of a conventional guard ring 10 used for holding a wafer in a heat treatment apparatus. As shown in FIG. 1A, the guard ring 10 has a doughnut-like form, which has a peripheral part 32 and a hollow part 31. Between the hollow part 31 and the peripheral part 32, an annular stage 33 is formed which is one step lower than the perimeter part 32. The guard ring 10 is generally formed of silicon carbide (SiC).
As shown in FIG. 1B, in the guard ring 10, which has the above-mentioned composition, a wafer 30 (not shown in FIG. 1A) is placed on the stage 33. The wafer 30 is heated by a light (heat ray) irradiated from the heat source (not shown) located above the wafer 30 in FIG. 1B at a temperature for applying a desired heat treatment.
Since the wafer 30 to be heat-treated is brought into surface-contact with the stage 33 of the guard ring 10, which has a comparatively large heat capacity, a temperature increasing rate of the peripheral edge of the wafer 30 is smaller than other portions of the wafer 30. Thereby, there is a problem in that a processing temperature becomes uneven in the heat treatment of the wafer 30.
In order to avoid such a problem, a guard ring 21 having a structure shown in FIG. 2 has been suggested. That is, as shown in FIG. 2, although the guard ring 21 has the same composition as the guard ring 10 shown in FIG. 1, convex parts (protrusions) 35 are provided on at least three positions of the stage 33 so that the wafer 30 is supported by the convex parts 35.
Therefore, since the wafer 30 contacts the guard ring 21 only at the convex parts 35, the above-mentioned influence, which is given to the wafer 30 by a large heat capacity of the guard ring 21, can be avoided.
However when the wafer 30 is separated from the stage 33 of the guard ring 21 as shown in FIG. 2, a radiation light 36 irradiated to heat the wafer 30 may enter the hollow part 31 of the guard ring 21 through a gap 34. Accordingly, in a heat treatment apparatus which measures a temperature of the heated wafer 30 by detecting a light radiated from the wafer 30 using a quartz rod 29 which is provided under the wafer 30 as shown in FIG. 2, a so-called stray light, which enters the hollow part 31 through the gap 34 as mentioned above may act as a noise in the detection of light by the quartz rod 29, which results in a problem in that the temperature of the wafer 30 cannot be measured with high accuracy.
It is a general object of the present invention to provide an improved and useful heat treatment apparatus in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide a heat treatment apparatus which can apply an accurate heat treatment to a wafer by performing an accurate measurement of a temperature of the wafer by a radiation thermometer.
Another object of the present invention is to provide a method of designing a heat treatment apparatus which can apply an accurate heat treatment to a wafer by performing an accurate measurement of a temperature of the wafer by a radiation thermometer.
In order to achieve the above-mentioned objects, there is provided according to one aspect of the present invention a heat treatment apparatus comprising: a heat source heating a substrate by irradiating a light on a first surface of the substrate; a support member supporting the substrate so that the first surface of the substrate faces the heat source and a predetermined gap is formed between a surface of the support member and a second surface of the substrate opposite to the first surface; and a temperature measuring device measuring a temperature of the substrate by detecting a light radiated from the second surface of the substrate by at least one light-detecting part facing the second surface of the substrate, wherein the substrate placed on the support member defines a first space on a side of the first surface of the substrate and a second space on a side of the second surface of the substrate, and the predetermined gap is configured and arranged so that an incident rate of a stray light entering the second space from the first space through the predetermined gap and incident on the light-detecting part is equal to or less than a predetermined value, where the incident rate is defined by a ratio of an amount of the stray light incident on the light-detecting part to an amount of light radiated by the heat source.
According to the above-mentioned invention, a light entering the second space through the predetermined gap between the substrate and the support member is prevented from being detected by the temperature measuring means as a noise. Thereby, the accuracy of the temperature measurement by the temperature measuring device can be improved, and the accuracy of the heat treatment applied to the substrate can be improved.
In the heat treatment apparatus according to the present invention, the support member may have a flat, annular shape with a plurality of protrusions formed on the surface thereof so that the substrate is placed on the protrusions and a width of the predetermined gap is defined by a height of the protrusions and a length of the predetermined gap is defined by an overlapping distance along which an outer peripheral part of the substrate overlaps with the support member, and a ratio of the overlapping distance of the substrate to the height of the protrusions may be determined based on the predetermined value of the incident rate.
Additionally, the heat source may comprise a plurality of halogen lamps, and the temperature measuring device may be a radiation thermometer having at least one quartz rod serving as the light-receiving part.
Additionally, there is provided according to another aspect of the present invention a method of designing a heat treatment apparatus comprising: a heat source heating a substrate by irradiating a light on a first surface of the substrate; a support member supporting the substrate so that the first surface of the substrate faces the heat source and a gap is formed between a surface of the support member and a second surface of the substrate opposite to the first surface; and a temperature measuring device measuring a temperature of the substrate by detecting a light radiated from the second surface of the substrate by at least one light-detecting part facing the second surface of the substrate, the method comprising the steps of: selecting a plurality of design values of the support member; calculating incidence rates of a stray light incident on the light-detecting part for a plurality of cases in which a plurality of the gaps defined by the selected design values are used, the stray light being radiated from the heat source and reaches the light-detecting part by traveling through the gap between the substrate and the support member; defining an approximation curve which approximates the calculated incidence rates for the design values of the support member; determining the design value of the support member which satisfies a maximum value of the incidence rate allowable for the heat treatment apparatus in accordance with the approximation curve; and designing the support member using the determined design value.
According to the above-mentioned invention, the support member of the heat treatment apparatus can be easily designed so that a light entering through the gap formed between the substrate and the support member is prevented from being incident on the light-detecting part of the temperature measuring device as a noise. Accordingly, an accurate heat treatment apparatus can be provided at a low cost.
In the above-mentioned method of designing a heat treatment apparatus, the support member may have a flat, annular shape with a plurality of protrusions formed on the surface thereof so that the substrate is placed on the protrusions and a width of the gap is defined by a height of the protrusions and a length of the gap is defined by an overlapping distance along which an outer peripheral part of the substrate overlaps with the support member, and the design value of the support member may be a ratio of the overlapping distance to the height of the protrusions.
Additionally, there is provided according to another aspect of the present invention a processor readable medium storing program code for causing a computer to design a support member of a heat treatment apparatus comprising: a heat source heating a substrate by irradiating a light on a first surface of the substrate; the support member supporting the substrate so that the first surface of the substrate faces the heat source and a gap is formed between a surface of the support member and a second surface of the substrate opposite to the first surface; and a temperature measuring device measuring a temperature of the substrate by detecting a light radiated from the second surface of the substrate by at least one light-detecting part facing the second surface of the substrate, the program code comprising: program code means for selecting a plurality of design values of the support member; program code means for calculating incidence rates of a stray light incident on the light-detecting part for a plurality of cases in which a plurality of the gaps defined by the selected design values are used, the stray light being radiated from the heat source and reaches the light-detecting part by traveling through the gap between the substrate and the support member; program code means for defining an approximation curve which approximates the calculated incidence rates for the design values of the support member; program code means for determining the design value of the support member which satisfies a maximum value of the incidence rate allowable for the heat treatment apparatus in accordance with the approximation curve; and program code means for designing the support member using the determined design value.
According to the processor readable medium of the present invention, since the above-mentioned design is realizable with software, a heat treatment apparatus can be designed still more easily.
Other objects, features and advantages of the present invention will become more apparent from the following detailed descriptions when read in conjunction with the accompanying drawings.